Q ... Quite often just before the release into the body of the song, you'll hear what sounds like a percussive hit (or sweep or swell) with a super long decay that just ends up sounding like white noise during the body of the song and this noise will continue till the end of a section where it is usually faded.

The question is, how do you tweak a sample so it will carry this characteristic without sounding as if its being looped?